The objective of this project is to investigate the effect of early abnormal visual experience on human accommodative vergence and accommodation. Subjects with functional amblyopia, with or without strabismus will be tested; matched controls will include normal subjects as well as those having strabismus without amblyopia. Static and dynamic measures will be made; static measures will be performed using a haploscope-optometer, while dynamic measures will be performed using continuous, infrared direct recording devices. Accommodative vergence will be measured in the occluded eye and accommodation will be measured in the viewing, stimulated eye, thus employing the classic accommodative vergence experimental paradigm of Mueller. Three sets of experiments will be conducted: (1) accommodative vergence and accommodative responses will be recorded upon stimulation of the amblyopic and fellow dominant eye to a variety of transient (pulses and steps), periodic (predictable sinusoids), and statistical (sum of sinusoids) inputs. Control systems approach will be used to study the input/output relationships, including use of Bode plots, with analysis carried out via a minicomputer, (2) accommodative vergence and accommodation will be recorded as a function of target spatial frequency upon stimulation of the amblyopic and fellow dominant eye, and (3) recovery of accommodative vergence and accommodation will be monitored as a function of orthoptics therapy for amblyopia, using stimuli and methods of analysis decribed in experiments 1 and 2 above. For all three experiments, an attempt will be made to correlate parameters of accommodative vergence and accommodation with such factors as visual acuity, eccentric fixation, contrast sensitivity, and versional abnormalities in the amblyopic eye.